Second: how, exactly, would that work? For the millionth time you cannot sell without a buyer. So if China is "dumping", someone else is buying. Or do you think they're just lighting these bonds on fire? Guess who wins in that scenario. Hint: not China.
You know, there's so much controversy about "fake news" lately, but the reality is that people will seek out the stories that fit their narrative, rather than looking at the data. Nobody to blame but ourselves.
This is well-reported in The Economist, Bloomberg, WSJ. The Chinese government is shoring up its currency due to capital injections in its SOEs and banks.
This isn't like the mid-1990s dump of the Rupiah; there isn't a malicious aspect to it. If it somehow were malicious, it would be pathetic because the U.S. dollar has increased in value over that time period.
Oct 2015 - Oct 2016 they've reduced their total holdings by ~139 billion. This could have been through either outright selling, or just letting them mature and not reinvesting, or some combination.
Either way that doesn't really look like dumping and is practically pocket change in the scheme of US debt.
